1. Field of the Invention
The present invention relates to a method and apparatus for separating a liquid into a permeate liquid and a residual liquid (i.e., a non-permeate liquid) using a membrane. In particular, the invention relates to a method and apparatus for isolating and recovering, using a membrane, target substances including valuable substances and impurities, such as salts and the like, contained in a liquid to be processed. Such a process is widely conducted in, for example, the fermentation industry, the pharmaceutical industry, the sugar refining industry, the amino acid industry, the food industry, the dye industry, the pigment industry, the chemical industry, the metal refining industry and the waste-disposal industry. Materials to be treated may be in a liquid or solid state. More particularly, in separation, removal and refinement of target substances in an treating liquid, the present invention relates to a method and apparatus for efficiently separating and recovering target substances from various liquids to be treated containing target substances in a combined process of contacting the liquids to be treated with, for example, a cleaning liquid or an extraction liquid and membrane separation.
In addition, the present invention relates to a method and apparatus for separating target substances having closely similar permeability using a separation membrane by achieving permeability desirable for separation with a selected separation membrane through management and control of separating processes and a membrane separation apparatus for effective demonstration of separating capability of the used separation membrane.
This application claims priority of Japanese Patent Application No. 2007-75655 filed Mar. 22, 2007, which is incorporated herein by reference.
The aforementioned present method of separating target substances using a membrane may be applied to refinement of polyglycerins, which are usually petrochemically-derived or oleochemically-derived. Polyglycerins exist in many forms, including a mixture of low polymerization polyglycerins, such as diglycerin and triglycerin, a mixture of higher polymerization polyglycerins and a mixture of cyclic polyglycerins and by-products. Attempts have been made to increase or decrease the proportion of specific components in the mixture, in addition, to fractionate the specific components. The fractionation and refinement methods using polyglycerin for this purpose are identified by molecular distillation purification, distillation under reduced pressure using a steam career and simulated moving bed chromatography and the like (for example, Patent Document 7).
2. Background Art
In the past, diafiltration (also referred to as “diawash”) using a membrane has been used in, for example, desalination of produced chemical dye and sugar refinement and is discussed in the references below.
For example, Patent Document 1 discloses a method of producing oligo syrup in which disaccharides, trisaccharides and even larger saccharides are obtained and a permeate liquid produced at a nanofiltration step is re-circulated. And describes a diafiltration process through nanofiltration that “in an aspect of the present invention, diafiltration also includes a nanofiltration step, in which water is added to a supply flow in a preferable amount corresponding to that of penetrant” (Patent Document [0036]).
Attempts have been made for effective diafiltration by selecting membranes according to target substances and operating a membrane device. For example, Patent Document 1 discloses, in Example 2 and Table 7, a result of a test that was “conducted in order to demonstrate the effects of changing the parameters on the filtering capability” (Patent Document, [0059] to [0064]).
In addition, A relationship between composition of a circulating liquid and composition of a permeate liquid in a membrane device has been presented as (for example, Non-Patent Document 3, Non-Patent Document 4).
Patent Document 1 also discloses, in Example 3 and Table 8, that “the results obtained on the penetrant (i.e., the permeate liquid) clearly demonstrate the influence of variation in the operating condition of the membrane separation apparatus. The obtained different flow rates of membrane permeation have provided different membrane selectivity for two compounds. All of the results demonstrate that the separation process may be changed and regulated”. Description, however, on a method of controlling selectivity (i.e., permeability) of target substances is not given (Patent Document 1[0064]).
In addition, in order to detect an end point of a diafiltration process using a membrane, measurement values have been used as indices. Patent Document 2 discloses “enzymatic decomposition of carbohydrate in protein fractionation.” Example 2 includes a description that “in order to fractionate carbohydrates and salts out of a protein extract, centrifugal supernatant is subject to ultrafiltration. The supernatant is concentrated to up to 5.5% DS and deionized water is added to the concentrated supernatant, which is then subject to diafiltration until the equation is satisfied: [permeate liquid (% DS)]/[residual liquid (% DS)]=0.09.”.
Although the disclosed process is not applied to control of permeability of target substances using a membrane, a method of providing an end point of a diafiltration process in terms of % DS, which is a measurement value (Patent Document 2).
In addition, attempts have been made to control extensive bioprocesses using analytical values. For example, Patent Document 3 discloses application to diafiltration using an ultrafiltration membrane and includes a description that “in the patent document regarding monitoring and control of a real time in situ biomanufacturing process in accordance with infrared spectroscopy, process monitoring and control using infrared spectroscopy in a refinement stage of biomanufacturing” is disclosed. (for example, Patent Document 3[0064] [0117]).
Furthermore, various process concepts of diafiltration have been variously studied. For example, the present applicant has disclosed a method using time difference multistage counter-current and a method of “recovering, after the supply of the treating liquid is stopped, a target substance in the system through multistage counter-current washing and separating operations” (Patent Document 5 and 6). Furthermore, other references describe a wide variety of process concepts of industrial diafiltration. Diafiltration is segmented and described in terms of: (1) batch diafiltration; (2) continuous (multistage) diafiltration; and (3) (continuous multistage) counter-current diafiltration (for example, Patent Document 5, 6 and Non-Patent Document 1).
Another reference describes diffusion models and solute permeation coefficients (Non-Patent Document 2).                [Patent Document 1] Published Japanese translation No. 2001-525177        [Patent Document 2] Published Japanese translation No. 2001-500734        [Patent Document 3] Published Japanese translation No. 2003-504638        [Patent Document 4] Japanese Unexamined Patent Application No. H5-117196        [Patent Document 5] Japanese Unexamined Patent Application No. H10-211423        [Patent Document 6] Japanese Unexamined Patent Application No. 2004-17035        [Patent Document 7] Japanese Patent Publication No. 3717193        [Non-Patent Document 1] Concept of Industrial-scale Diafiltration Systems, Desalination 144 (2002) 179-184 Frank Lipnizki et al.        [Non-Patent Document 2] Haruhiko Oya and Atsuo Watanabe ed., “Food membrane technology: Guidance to membrane technology” Korin Publishing Co., Ltd., Tokyo, 1999, 9th issue, pages 25 and 32        [Non-Patent Document 3] Analysis of Solutes Rejection in Ultrafiltration, Journal of Chemical Engineering of Japan Vol. 14, No. 1 (1981) 32˜37 Shin-ichi Nakao et al.        [Non-Patent Document 4] Purification of Oligosaccharides by Nanofiltration Journal of Membrane Science Vol. 209 Issue 1 (2002) 321˜335 Athanasios K. Goulas et al.        